Current collector, method for preparing current collector, pole piece, lithium ion battery and electric device

Abstract

The invention relates to the technical field of batteries, and particularly discloses a current collector, a method for preparing the current collector, a pole piece, a lithium ion battery and a power utilization device.The current collector comprises a base material and a conductive coating arranged on at least one side of the base material, and physical crosslinking points are evenly distributed in the conductive coating; the physical cross-linking points are non-covalent bond connecting points and comprise coordinate bonds between the binder and metal ions and / or hydrogen bonds between the binder and the polyhydroxy compound. The physical cross-linking points can effectively improve the adaptability of the conductive coating to the expansion and shrinkage stress of the active material layer in the long-term circulation process, the physical cross-linking points can be self-generated again after being damaged, the cross-linking structure improves the adhesion strength of the conductive coating to the current collector, meanwhile, the conductive coating has excellent fatigue resistance, and the service life of the conductive coating is prolonged. After long-term circulation, the high cohesiveness is still kept, and the phenomena of interface separation and active substance powder falling are not prone to occurring.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a current collector, a method for preparing a current collector, an electrode sheet, a lithium-ion battery, and an electric device. Background Art

[0002] The current collector plays a crucial role in power batteries. The current collector collects and conducts the electrons generated by the internal chemical reaction of the battery to the outside of the battery and is connected to the charge load, thereby realizing the conversion of chemical energy into electrical energy. In lithium-ion power batteries, copper foil and aluminum foil are usually used as current collectors. The positive and negative electrode slurries are coated on the surface of the current collector and dried to form an active material layer. The current collector and the active material layer play roles of electron transfer, heat conduction, and mechanical support through direct contact. Sufficient contact between the current collector and the active material layer can strengthen electron and heat transfer and give full play to the performance of the battery cell.

[0003] Related technologies usually coat a carbon material layer on the surface of the current collector to enhance the contact interface between the current collector and the active material layer. Coating carbon on the current collector can improve the material contact interface, enhance the coating adhesion strength, protect the current collector from being corroded by the electrolyte, increase the battery energy density, inhibit battery polarization, reduce the battery internal resistance, increase the battery cycle life, and improve the battery rate performance. However, the adhesion strength of the carbon material layer to the current collector is insufficient and the fatigue resistance is poor, and interface separation and active material powder falling are likely to occur after long-term cycling. Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems in the related technologies to some extent. For this purpose, an object of the present invention is to provide a current collector, which includes a conductive coating having high adhesion strength to a current collector substrate and excellent fatigue resistance, and still maintains high adhesiveness after long-term cycling, and is not likely to have interface separation and active material powder falling.

[0005] Specifically, a first aspect of the present invention provides a current collector, including a substrate and a conductive coating provided on at least one side of the substrate; the conductive coating includes at least one of a polyhydroxy compound and a metal ion, a binder, and a conductive agent; the binder includes a water-soluble polymer containing a polar group, and the polar group contains one or more of O atom, S atom, and N atom.

[0006] In the conductive coating of the present invention, there are uniformly distributed physical cross-linking points, and the physical cross-linking points are non-covalent bond connection points, including coordination bonds between the binder and metal ions and / or hydrogen bonds between the binder and polyhydroxy compounds. Such physical cross-linking points can effectively improve the adaptability of the conductive coating to the expansion and contraction stress of the active material layer during long-term cycling. After the physical cross-linking points are damaged, they can regenerate spontaneously. This cross-linked structure improves the adhesion strength of the conductive coating to the current collector, and at the same time endows the conductive coating with excellent fatigue resistance, still maintaining high adhesiveness after long-term cycling, and not easily showing interface separation and active material powder falling off phenomena.

[0007] According to some embodiments of the present invention, the polar groups include at least one of -COOH, -COO - , -CN, -NH2.

[0008] According to some embodiments of the present invention, the binder includes one or more of polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, acrylic acid-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-acrylate copolymer.

[0009] According to some embodiments of the present invention, in the binder, the proportion of the number of polar groups to the total number of functional groups is 40% - 100%.

[0010] According to some embodiments of the present invention, the polyhydroxy compound includes polyol and polyphenol; the polyol includes water-soluble polyol; the water-soluble polyol includes one or more of xylitol, sorbitol, polyvinyl alcohol; the polyphenol includes water-soluble polyphenol; the water-soluble polyphenol includes tannic acid.

[0011] According to some embodiments of the present invention, the metal ions include one or more of metal ions of the second main group, metal ions of the third main group, and transition metal ions.

[0012] According to some embodiments of the present invention, the metal ions include Zn 2+ , Ca 2+ , Mg 2+ , Cu 2+ , Fe 3+ , Al 3+ or one or more of them.

[0013] According to some embodiments of the present invention, the metal ions are added to the conductive coating in the form of water-soluble metal salts, and the solid mass ratio of the conductive agent, binder, water-soluble metal salt, and polyhydroxy compound is 100: (15 - 120): (0 - 5): (0 - 10).

[0014] According to some embodiments of the present invention, the solid mass ratio of the conductive agent, binder, water-soluble metal salt, and polyhydroxy compound is 100: (15 to 120): (0.2 to 5): (3 to 10).

[0015] According to some embodiments of the present invention, the conductive coating further includes a dispersant, and the dispersant includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, sodium carboxymethyl cellulose, polyacrylamide, and polyacrylic acid copolymers; the mass of the dispersant is 5% - 30% of the mass of the conductive agent.

[0016] According to some embodiments of the present invention, the conductive agent includes one or more of acetylene black, carbon black, layered graphite, graphene, and carbon nanotubes; the thickness of the conductive coating is 0.5 μm - 3 μm.

[0017] The second aspect of the present invention provides a method for preparing the current collector of the first aspect of the present invention, including the following steps: Disperse at least one of the polyhydroxy compound and the water-soluble metal salt, the binder, and the conductive agent in an aqueous solvent to obtain a conductive paste; Coat the conductive paste on at least one side of the substrate, and after drying, obtain the current collector.

[0018] The preparation process of the current collector of the present invention is simple, with few steps, and is suitable for large-scale industrial promotion.

[0019] According to some embodiments of the present invention, the conductive paste further includes a dispersant, and the preparation of the conductive paste includes: dispersing at least one of the polyhydroxy compound and the water-soluble metal salt, the binder, the conductive agent, and the dispersant in an aqueous solvent.

[0020] According to some embodiments of the present invention, the water-soluble metal salt includes one or more of nitrates, sulfates, and chlorides; the water-soluble metal salt includes Zn 2+ , Ca 2+ , Mg 2+ , Cu 2+ , Fe 3+ , Al 3+ one or more of; the aqueous solvent includes water; the pH of the conductive paste is 4 - 9; the solid mass ratio of the conductive agent, binder, water-soluble metal salt, and polyhydroxy compound is 100 : (15 to 120): (0 to 5): (0 to 10); the solid content of the conductive paste is 2% - 20%.

[0021] The third aspect of the present invention provides a pole piece, including the current collector of the first aspect of the present invention. Due to the adoption of the current collector of the first aspect of the present invention, the pole piece of the present invention has all the advantages of the current collector, which will not be elaborated here.

[0022] In the fourth aspect of the present invention, a lithium-ion battery is provided, which includes the electrode sheet of the third aspect of the present invention. Since the current collector of the first aspect of the present invention is adopted, the lithium-ion battery of the present invention has all the advantages of the current collector, which will not be elaborated herein.

[0023] In the fifth aspect of the present invention, an electrical device is provided, which includes the lithium-ion battery of the fourth aspect of the present invention. Since the current collector of the first aspect of the present invention is adopted, the electrical device of the present invention has all the advantages of the current collector, which will not be elaborated herein.

[0024] The additional aspects and advantages of the present invention will be partly given in the following description, partly become apparent from the following description, or be understood through the practice of the present invention. Detailed Embodiments

[0025] Embodiments of the present invention will be described in detail below. The following described embodiments are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0026] In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more. The meaning of "a variety" is two or more. In this article, the term "comprising" or "including" is an open expression, that is, it includes the content specified by the present invention, but does not exclude other aspects.

[0027] In the ranges disclosed herein, the endpoints and any values are not limited to the exact range or value. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0028] The current collector plays a crucial role in power batteries. The current collector collects and conducts the electrons generated by the internal chemical reactions of the battery to the outside of the battery and is connected to the charge load, thereby realizing the conversion of chemical energy into electrical energy. Copper foils and aluminum foils are usually used as the current collectors in lithium-ion power batteries. The positive and negative electrode slurries are coated on the surface of the current collector, and after drying, an active material layer is formed. The current collector and the active material layer play roles in electron transfer, heat conduction, and mechanical support through direct contact. Sufficient contact between the current collector and the active material layer can strengthen electron and heat transfer and give full play to the performance of the battery cell.

[0029] Related technologies usually coat a layer of carbon material on the surface of the current collector to enhance the contact interface between the current collector and the active material layer. Carbon coating of the current collector can improve the material contact interface, enhance the bonding strength of the coating, protect the current collector from being corroded by the electrolyte, increase the battery energy density, inhibit battery polarization, reduce the battery internal resistance, increase the battery cycle life, and improve the battery rate performance. However, the carbon material layer has insufficient adhesion strength to the current collector and poor fatigue resistance, and is prone to interface separation and active material powdering after long-term cycling.

[0030] In order to solve the above problems, the present invention proposes a current collector, which includes a conductive coating, and there are uniformly distributed physical crosslinking points in the conductive coating. The physical crosslinking points are non-covalent bond connection points, including coordination bonds between the binder and the metal ions and / or hydrogen bonds between the binder and the polyhydroxy compound. Such physical crosslinking points can effectively improve the adaptability of the conductive coating to the expansion and contraction stress of the active material layer during long-term cycles. The physical crosslinking points can be regenerated spontaneously after being destroyed. This crosslinking structure improves the adhesion strength of the conductive coating to the current collector, and at the same time, the conductive coating has excellent fatigue resistance, and still maintains high adhesion after long-term cycles, and is not prone to interface separation and active material powdering.

[0031] Specifically, the first aspect of the present invention provides a current collector, comprising a substrate and a conductive coating arranged on at least one side of the substrate; the conductive coating comprises at least one of a polyhydroxy compound and metal ions, a binder and a conductive agent; the binder comprises a water-soluble polymer containing a polar group, and the polar group contains one or more of an O atom, a S atom, and a N atom.

[0032] The metal coordination bonds and hydrogen bonds in the conductive coating of the present invention are non-covalent bonds. When the bonding network is subjected to external forces, this non-covalent weak bonding network will be deformed first. The chain breaking based on the coordination bonds and / or hydrogen bonds can dissipate a large amount of energy, while providing more mobile space for the polymer, releasing the hidden length, maintaining the integrity of the bonding network, and avoiding the bonding network from being destroyed and failing, so that the conductive coating has excellent fatigue resistance. At the same time, the polar groups in the binder can increase the force on the surface of the current collector substrate, thereby improving the adhesion strength of the conductive coating to the current collector.

[0033] In some embodiments, the polar group contains at least one of an O atom and a N atom. These atoms contain lone pairs of electrons after forming bonds with other atoms and have high electronegativity, so the polar group containing these atoms can form hydrogen bonds with hydroxyl groups in polyhydroxy compounds and form coordination bonds with metal ions.

[0034] In some embodiments, the polar groups include -COOH, -COO -, -CN, -NH2, or at least one of them. These polar groups have a stronger ability to form hydrogen bonds with the hydroxyl groups in the polyhydroxy compound and coordination bonds with metal ions, thus enabling the formation of an effective weak bonding network of non-covalent bonding, which is beneficial to maintaining the integrity of the bonding network. In addition, the carboxyl groups in the binder can exist in the form of coordination salts, which have extremely low solubility in the electrolyte, can effectively reduce the swelling of the coating in the electrolyte, and maintain the stability of the bonding network.

[0035] In some embodiments, the binder includes one or more of polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, acrylic acid-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-acrylate copolymer. The metal ions of the present invention need to be provided by the dissociation of metal salts in water. Therefore, the conductive paste for preparing the conductive coating is usually an aqueous paste. These binders used in the present invention are all water-soluble binders, containing -COOH, -COO - , -CN polar groups, are soluble in water, can form coordination bonds with metal ions in the paste well and form hydrogen bonds with the hydroxyl groups in the polyhydroxy compound. The "salt" here can be a potassium salt or a sodium salt. For example, polyacrylate is sodium polyacrylate.

[0036] In some embodiments, the weight average molecular weight of the binder can be 5000 Dalton - 500000 Dalton, such as 5000 Dalton, 10000 Dalton, 50000 Dalton, 100000 Dalton, 150000 Dalton, 200000 Dalton, 250000 Dalton, 300000 Dalton, 350000 Dalton, 400000 Dalton, 450000 Dalton or 500000 Dalton.

[0037] In some embodiments, in the binder, the proportion of the number of the polar groups in the total number of functional groups can be 40% - 100%. The more the number of the polar groups, the more beneficial it is to form more physical cross-linking points, the easier it is to maintain the integrity of the bonding network, and further the more beneficial it is to improve the adhesion strength of the conductive coating to the current collector and the fatigue resistance of the conductive coating.

[0038] In some specific embodiments, the proportion of the number of the polar groups in the total number of functional groups can be 40%, 50%, 60%, 70%, 80%, 90% or 100%.

[0039] In some embodiments, the binder raw material used is in the form of a glue solution. The pH of the binder can be 3 - 9, for example, it can be 3, 4, 5, 6, 7, 8, or 9. Neither the acidity nor the alkalinity of the binder can be too strong, otherwise it will corrode the current collector substrate, which is not conducive to electron collection and will also reduce the service life of the battery. The solid content of the binder can be 10% - 30%, for example, 10%, 15%, 20%, 25%, or 30%.

[0040] In some embodiments, the polyhydroxy compound includes polyols and polyphenols. The polyols include water-soluble polyols. The water-soluble polyols include one or more of xylitol, sorbitol, and polyvinyl alcohol; the polyphenols include water-soluble polyphenols. The water-soluble polyphenols include tannic acid. The above polyols and polyphenols have good solubility in aqueous solvents and can form hydrogen bonds with the polar groups in the binder in the conductive paste used to prepare the conductive coating, thereby improving the adhesion strength of the conductive coating to the current collector substrate and its fatigue resistance.

[0041] In some embodiments, the metal ions include one or more of Group IIA metal ions, Group IIIA metal ions, and transition metal ions. Thus, the metal ions form metal coordination bonds with the polar groups in the binder, improving the adhesion strength of the conductive coating to the current collector substrate and its fatigue resistance.

[0042] In some specific embodiments, the metal ions include Zn 2+ 、Ca 2+ 、Mg 2+ 、Cu 2+ 、Fe 3+ 、Al 3+ or one or more of them. Compared with monovalent metal ions, using divalent metal ions for coordination has a more significant effect on improving the adhesion strength to the current collector substrate.

[0043] In some embodiments, the metal ions are added to the conductive coating in the form of water-soluble metal salts, and the solid mass ratio of the conductive agent, binder, water-soluble metal salt, and polyhydroxy compound can be 100 : (15 - 120) : (0 - 5) : (0 - 10). In this ratio relationship, the binder and other components are calculated by mass in solid form, so the mass ratio between these components is the solid mass ratio.

[0044] In some specific embodiments, the solid mass ratio of the conductive agent, binder, water-soluble metal salt, and polyhydroxy compound can be 100 : 20 : 2.5 : 5, 100 : 100 : 2.5 : 10, or 100 : 85 : 5 : 6.5.

[0045] In some specific embodiments, the solid mass ratio of the conductive agent, binder, water-soluble metal salt, and polyhydroxy compound may be 100 : (15 - 120) : (0.1 - 5) : (0.1 - 10) or 100 : (15 - 120) : (0.2 - 5) : (3 - 10). The conductive coating contains both metal ions and polyhydroxy compounds, which can not only form metal coordination bonds but also form hydrogen bonds, thus facilitating the formation of a non-covalent binding weak bonding network, maintaining the integrity of the bonding network, and improving the adhesion strength of the conductive coating to the current collector substrate and its fatigue resistance.

[0046] In some embodiments, the conductive coating further includes a dispersant. The dispersant includes one or more of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC-Na), polyacrylamide (PAM), and polyacrylic acid copolymer (PAA). The above dispersants can play a preliminary dispersion role, have good solubility in aqueous solutions, and have excellent affinity for carbon materials, which is beneficial to improving the uniformity of the conductive paste, thereby improving the uniformity of the conductive coating, avoiding low local adhesion strength and poor fatigue resistance of the conductive coating, resulting in local interface separation and active material powder falling, and at the same time reducing the resistance of the electrode sheet.

[0047] In some embodiments, the mass of the dispersant may be 5% - 30% of the mass of the conductive agent, such as 5%, 10%, 15%, 20%, 25%, or 30%. If the amount of the dispersant is too small, it cannot achieve the effect of uniformly dispersing the conductive paste. If the amount of the dispersant is too large, it may lead to a decrease in the conductivity and processability of the conductive coating. Therefore, the amount of the dispersant is preferably within the above range.

[0048] In some embodiments, the conductive agent includes one or more of acetylene black, carbon black, lamellar graphite, graphene, and carbon nanotubes. The above conductive agents can achieve the conductivity of the conductive coating, reduce the contact resistance between the current collector and the active material layer, and improve the internal electron transfer path of the electrode sheet.

[0049] In some embodiments, the thickness of the conductive coating may be 0.5 μm - 3 μm, such as 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm. If the conductive coating is too thin, the improvement effect on the contact interface between the current collector and the active material layer is not good; if the conductive coating is too thick, it may lead to a decrease in the energy density of the battery and a deterioration of the mechanical properties of the electrode sheet. Therefore, the thickness of the conductive coating is preferably within the above range.

[0050] In some embodiments, the current collector may be a positive current collector. The positive current collector may be a conventional metal foil or a composite current collector (a composite current collector can be formed by disposing a metal material on a polymer substrate). As an example, the positive current collector may be an aluminum foil. Functional groups such as carboxyl and cyano groups in the binder have strong metal ion coordination effects and can chelate metal ions in a multi-coordination form. When applied to the positive current collector, it can effectively prevent the dissolution of Fe elements in the active material, and at the same time, it can also chelate the metal ions dissolved due to the corrosion of the current collector, protect the current collector, improve the adhesion strength between the conductive coating and the current collector, and enhance the battery safety.

[0051] In some embodiments, the current collector may be a negative current collector. The negative current collector may be a conventional metal foil or a composite current collector (for example, a composite current collector can be formed by disposing a metal material on a polymer substrate). As an example, the negative current collector may be a copper foil.

[0052] The second aspect of the present invention provides a method for preparing the current collector of the first aspect of the present invention, including the following steps: Disperse at least one of a polyhydroxy compound and a water-soluble metal salt, a binder, and a conductive agent in an aqueous solvent to obtain a conductive paste; Coat the conductive paste on at least one side of a substrate, and after drying, obtain the current collector.

[0053] The preparation process of the current collector of the present invention is simple, with few steps, and is suitable for large-scale industrial promotion.

[0054] In some embodiments, the conductive paste further includes a dispersant, and the preparation of the conductive paste includes: dispersing at least one of a polyhydroxy compound and a water-soluble metal salt, a binder, a conductive agent, and a dispersant in an aqueous solvent.

[0055] In some embodiments, the water-soluble metal salt includes one or more of nitrates, sulfates, and chlorides; the water-soluble metal salt includes Zn 2+ 、Ca 2+ 、Mg 2+ 、Cu 2+ 、Fe 3+ 、Al 3+ one or more of.

[0056] In some specific embodiments, the water-soluble metal salt includes one or more of zinc chloride, calcium chloride, iron chloride, magnesium chloride, copper chloride, aluminum chloride, zinc sulfate, iron sulfate, magnesium sulfate, copper sulfate, zinc nitrate, calcium nitrate, magnesium nitrate, copper nitrate, and aluminum nitrate.

[0057] In some embodiments, the aqueous solvent includes water. To improve solubility and dispersibility, the aqueous solvent may further include an appropriate amount of an organic solvent such as ethanol.

[0058] In some embodiments, the pH of the conductive paste may be 4 - 9, such as 4, 5, 6, 7, 8, or 9. The pH of the paste can be adjusted by changing the type of binder, the addition amount, or by adding a pH regulator. The pH regulator can be a weak acid or a weak base, and the addition amount is adjusted according to the pH of the paste. The acidity or alkalinity of the conductive paste should not be too strong to avoid corroding the current collector substrate. The solid content of the conductive paste can be 3% - 10%, such as 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. The viscosity of the conductive paste can be 100 mPa·s - 1000 mPa·s, such as 100 mPa·s, 200 mPa·s, 300 mPa·s, 400 mPa·s, 500 mPa·s, 600 mPa·s, 700 mPa·s, 800 mPa·s, 900 mPa·s, or 1000 mPa·s.

[0059] In some embodiments, the solid mass ratio of the conductive agent, binder, water-soluble metal salt, and polyhydroxy compound is 100 : (15 - 120) : (0 - 5) : (0 - 10). The solid content of the conductive paste is 2% - 20%.

[0060] In some embodiments, the solid mass ratio of the conductive agent, dispersant, binder, water-soluble metal salt, and polyhydroxy compound can be 100 : (5 - 30) : (15 - 120) : (0 - 5) : (0 - 10). The solid content of the conductive paste is 2% - 20%.

[0061] In some embodiments, the method for preparing the current collector includes the following steps: Add the dispersant to a part of the aqueous solvent (35% - 55% of the total amount), and completely dissolve the dispersant by stirring (such as vacuum high-speed mechanical stirring) to obtain a mixed solution; add the conductive agent to the mixed solution and continue stirring to obtain a conductive agent dispersion suspension; Grind and mix the conductive agent dispersion suspension, binder, and the remaining aqueous solvent (45% - 65% of the total amount) to obtain a finely ground conductive agent dispersion suspension. The grinding and mixing can be carried out in a grinder such as a sand mill. The grinding medium can be zircon beads, the diameter of the zircon beads in the sand mill is 0.1 mm - 3 mm, the rotation speed is 800 rpm - 2000 rpm, and the sanding time is 0.5 h - 3 h; Mix the finely ground conductive agent dispersion suspension with the water-soluble metal salt and polyhydroxy compound, and mix by stirring (such as vacuum high-speed mechanical stirring) to obtain a conductive paste; Coat the conductive paste onto the current collector substrate to form a paste layer with a viscosity of 100 - 1000 mPa·s and a thickness of 700 nm - 10 μm; After drying, the current collector is obtained, wherein the thickness of the conductive coating is 0.5 μm - 3 μm, and a three-dimensional network structure with high adhesion strength having physical cross-linking points is formed.

[0062] The third aspect of the present invention provides an electrode sheet including the current collector of the first aspect of the present invention. Due to the adoption of the current collector of the first aspect of the present invention, the electrode sheet of the present invention has all the advantages of the current collector, which will not be elaborated herein.

[0063] The fourth aspect of the present invention provides a lithium-ion battery including the electrode sheet of the third aspect of the present invention. Due to the adoption of the current collector of the first aspect of the present invention, the lithium-ion battery of the present invention has all the advantages of the current collector, which will not be elaborated herein.

[0064] The fifth aspect of the present invention provides an electrical device including the lithium-ion battery of the fourth aspect of the present invention. Due to the adoption of the current collector of the first aspect of the present invention, the electrical device of the present invention has all the advantages of the current collector, which will not be elaborated herein.

[0065] The following will explain the solution of the present invention in combination with embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the embodiments regarding specific techniques or conditions, they shall be carried out according to the techniques or conditions described in the literature in the art or according to the product specifications. For reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0066] Example 1 (1) First, prepare a conductive paste, the raw materials of which include acetylene black, sodium carboxymethyl cellulose, polyacrylic acid (the proportion of polar groups in the total functional groups is 100%, and the weight-average molecular weight is 280,000 Dalton), zinc chloride, and tannic acid, and the mass ratio is 100:10:85:0.5:5 in sequence, and the solid content of the conductive paste is 10%. The preparation method of the conductive paste specifically includes the following steps: Add sodium carboxymethyl cellulose to deionized water with 50% of the total water volume, stir at 1000 rpm for 1 h to completely dissolve sodium carboxymethyl cellulose; then add the conductive agent acetylene black, disperse in a sand mill at 2000 rpm for 2 h, then add polyacrylic acid and the remaining 50% of deionized water, and continue to disperse for 2.5 h; finally add zinc chloride and tannic acid, and disperse at 1000 rpm for 0.5 h to obtain a conductive paste with a pH of 6 - 8.

[0067] (2) Coat the above conductive paste on both sides of the aluminum foil current collector through a gravure roll coater, and after drying, a carbon-coated aluminum foil is obtained, and the thickness of the conductive coating is 1.5 ± 0.3 μm.

[0068] (3) Prepare the positive electrode slurry: Mix lithium iron phosphate, conductive carbon black, carbon nanotubes, polyvinylidene fluoride, and N-methylpyrrolidone according to a mass ratio of 100:0.6:3:2.5:50, and stir at 2000 rpm for 2 h to obtain the positive electrode slurry.

[0069] (4) Coat the above positive electrode slurry on the above carbon-coated aluminum foil, control the double-sided surface density of the positive electrode to be 400 g / m 2 , dry at 120 °C, and obtain the positive electrode sheet after rolling and slitting.

[0070] Example 2 Prepare the carbon-coated aluminum foil and the positive electrode sheet according to the method described in Example 1, except that the raw materials of the conductive slurry include acetylene black, sodium carboxymethyl cellulose, polyacrylic acid (the proportion of polar groups in the total functional groups is 100%, and the weight average molecular weight is 280,000 daltons), calcium chloride, and tannic acid, and the mass ratio is 100:10:85:0.42:5 in sequence. The solid content of the conductive slurry is 10%, and the pH of the conductive slurry is 6-8.

[0071] Example 3 Prepare the carbon-coated aluminum foil and the positive electrode sheet according to the method described in Example 1, except that the raw materials of the conductive slurry include acetylene black, sodium carboxymethyl cellulose, polyacrylic acid (the proportion of polar groups in the total functional groups is 100%, and the weight average molecular weight is 280,000 daltons), ferric chloride, and tannic acid, and the mass ratio is 100:10:85:0.6:5 in sequence. The solid content of the conductive slurry is 10%, and the pH of the conductive slurry is 6-8.

[0072] Example 4 Prepare the carbon-coated aluminum foil and the positive electrode sheet according to the method described in Example 1, except that the raw materials of the conductive slurry include acetylene black, sodium carboxymethyl cellulose, polyacrylic acid (the proportion of polar groups in the total functional groups is 100%, and the weight average molecular weight is 280,000 daltons), zinc chloride, and xylitol, and the mass ratio is 100:10:85:0.5:0.45 in sequence. The solid content of the conductive slurry is 10%, and the pH of the conductive slurry is 6-8.

[0073] Example 5 Prepare the carbon-coated aluminum foil and the positive electrode sheet according to the method described in Example 1, except that the raw materials of the conductive slurry include acetylene black, sodium carboxymethyl cellulose, polyacrylic acid (the proportion of polar groups in the total functional groups is 100%, and the weight average molecular weight is 280,000 daltons), sodium hydroxide, and tannic acid, and the mass ratio is 100:10:85:0.5:5 in sequence. The solid content of the conductive slurry is 10%, and the pH of the conductive slurry is 6-8.

[0074] Example 6 The carbon-coated aluminum foil and the positive electrode sheet are prepared according to the method described in Example 1, except that the raw materials of the conductive paste include acetylene black, sodium carboxymethyl cellulose, polyacrylic acid (the proportion of polar groups in the total number of functional groups is 100%, and the weight-average molecular weight is 280,000 daltons), zinc chloride, and the mass ratio is 100:10:85:0.5 in sequence. The solid content of the conductive paste is 10%, and the pH of the conductive paste is 6-8.

[0075] Example 7 The carbon-coated aluminum foil and the positive electrode sheet are prepared according to the method described in Example 1, except that the raw materials of the conductive paste include acetylene black, sodium carboxymethyl cellulose, polyacrylic acid (the proportion of polar groups in the total number of functional groups is 100%, and the weight-average molecular weight is 280,000 daltons), tannic acid, and the mass ratio is 100:10:85:5 in sequence. The solid content of the conductive paste is 10%, and the pH of the conductive paste is 6-8.

[0076] Example 8 The carbon-coated aluminum foil and the positive electrode sheet are prepared according to the method described in Example 1, except that sodium polyacrylate (the proportion of polar groups in the total number of functional groups is 100%, and the weight-average molecular weight is 310,000 daltons) is used to replace polyacrylic acid. The pH of the conductive paste is 6-8.

[0077] Example 9 The carbon-coated aluminum foil and the positive electrode sheet are prepared according to the method described in Example 1, except that acrylic acid-acrylonitrile copolymer (the proportion of polar groups in the total number of functional groups is 100%, purchased from Sichuan Yindi Le Material Technology Group Co., Ltd., model LA-136D) is used to replace polyacrylic acid. The pH of the conductive paste is 6-8.

[0078] Example 10 The carbon-coated aluminum foil and the positive electrode sheet are prepared according to the method described in Example 1, except that polyvinyl alcohol (the proportion of polar groups in the total number of functional groups is 100%, and the weight-average molecular weight is 8,000 daltons) is used to replace tannic acid. The pH of the conductive paste is 6-8.

[0079] Example 11 The carbon-coated aluminum foil and the positive electrode sheet are prepared according to the method described in Example 1, except that acetylene black, sodium carboxymethyl cellulose, polyacrylic acid (the proportion of polar groups in the total number of functional groups is 100%, and the weight-average molecular weight is 280,000 daltons), zinc chloride, tannic acid, and the mass ratio is 100:20:100:0.5:5 in sequence. The pH of the conductive paste is 6-8.

[0080] Example 12 The carbon-coated aluminum foil and the positive electrode sheet were prepared according to the method described in Example 1, except that sodium carboxymethyl cellulose was not used. The pH of the conductive paste was 6 - 8.

[0081] Example 13 The carbon-coated aluminum foil and the positive electrode sheet were prepared according to the method described in Example 1, except that the pH of the conductive paste was 2, and 0.1 mol / L oxalic acid was added to the prepared conductive paste until the target pH value was reached.

[0082] Example 14 The carbon-coated aluminum foil and the positive electrode sheet were prepared according to the method described in Example 1, except that the pH of the conductive paste was 11, and 25% ammonia water was added to the prepared conductive paste until the target pH value was reached.

[0083] Comparative Example 1 The carbon-coated aluminum foil and the positive electrode sheet were prepared according to the method described in Example 1, except that the raw materials of the conductive paste included acetylene black, sodium carboxymethyl cellulose, and polyacrylic acid (the proportion of polar groups in the total functional groups was 100%, and the weight-average molecular weight was 280,000 Dalton), and the mass ratio was 100:10:85 in sequence. The solid content of the conductive paste was 10%, and the pH of the conductive paste was 6 - 8.

[0084] Comparative Example 2 The carbon-coated aluminum foil and the positive electrode sheet were prepared according to the method described in Example 1, except that styrene-butadiene rubber (SBR) was used to replace polyacrylic acid. The pH of the conductive paste was 6 - 8.

[0085] Performance Test of the Electrode Sheet (1)Peeling Strength Test of the Positive Electrode Sheet The peeling strength test was carried out according to GB / T 2792-2014. The test results are shown in Table 1.

[0086] (2)Resistivity Test of the Positive Electrode Sheet The resistivity of the electrode sheet was tested using an electrode resistance meter at a temperature of 25°C and a probe pressure of 25 MPa. The test results are shown in Table 1.

[0087] (3)Fatigue Resistance Test of the Positive Electrode Sheet The fatigue resistance test of the positive electrode sheet was carried out by applying the above positive electrode sheet to a lithium-ion battery, charging / discharging at a rate of 1C / 1C, disassembling the battery after 600 cycles, and measuring the peeling strength of the electrode sheet for comparison.

[0088] The lithium-ion battery is composed of the above-mentioned positive electrode sheet, negative electrode sheet, a polypropylene separator with a thickness of 20 μm, and a LiPF6 electrolyte. The corresponding negative electrode sheet includes a current collector and a negative electrode active material layer coated on the current collector. The current collector is a shiny copper foil. The negative electrode active material layer is prepared by mixing artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene latex, and water in a mass ratio of 100:1:1.5:2.5:100.

[0089] After disassembling the cycled battery, the peel strength of the positive electrode sheet was tested, and the test results are shown in Table 1.

[0090] Table 1

[0091] Results and Discussion: As can be seen from Table 1, by comparing Examples 1-3 with Comparative Example 1, through the addition of divalent and trivalent metal ions and polyol tannic acid, the peel strength of the electrode sheet increases, indicating that the formation of metal ion coordination bonds and hydrogen bonds can improve the bonding strength between the aluminum foil and the conductive coating. The small change in the electrode sheet resistance indicates that the dispersion of the conductive agent particles is not affected by physical cross-linking bonds such as coordination bonds and hydrogen bonds.

[0092] For Comparative Example 1 and Comparative Example 2, in Example 1, a binder containing polar groups was used, which can form a non-covalent weak bonding network with metal salts and polyhydroxy compounds, improving the adhesion strength of the conductive coating to the current collector substrate and its fatigue resistance.

[0093] By comparing Example 1 and Example 5, Example 1 has a higher peel strength and a lower electrode sheet resistance, indicating that the promotion effect of the divalent metal ion coordination of the present application on the peel strength of the electrode sheet is more prominent than that of the monovalent metal ion, and the dispersion effect of the conductive agent is better, and the electrode sheet resistance is lower.

[0094] By comparing Example 1 and Example 6, Example 1 has a higher peel strength, indicating that the addition of tannic acid to form hydrogen bond interactions in the present application has a positive effect on enhancing the peel strength and fatigue resistance of the electrode sheet.

[0095] By comparing Example 1 and Example 7, Example 1 has a higher peel strength, indicating that the addition of soluble metal salts to form coordination bonds in the present application has a positive effect on enhancing the peel strength and fatigue resistance of the electrode sheet.

[0096] By comparing Example 1 and Example 12, Example 1 has a higher peel strength and a lower electrode sheet resistance, indicating that the addition of a dispersant in the present application is beneficial to the formation of a uniform coating, and the dispersion effect of the conductive agent is better.

[0097] Comparing Comparative Example 1 with Examples 13-14, Example 1 has higher peel strength and lower electrode sheet resistance, indicating that the excessive acidity or alkalinity of the conductive paste corrodes the aluminum foil, resulting in a decrease in the adhesion strength of the conductive coating to the aluminum foil and an increase in the electrode sheet resistance.

[0098] In the description of this specification, the descriptions referring to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples.

[0099] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A current collector, characterized in that, It includes a substrate and a conductive coating provided on at least one side of the substrate; the conductive coating includes at least one of a polyhydroxy compound and metal ions, as well as a binder and a conductive agent; the binder includes a water-soluble polymer containing polar groups, and the polar groups contain one or more of O atoms, S atoms, and N atoms.

2. The current collector according to claim 1, wherein The polar groups include at least one of -COOH, -COO - , -CN, and -NH2.

3. The current collector according to claim 1, wherein The binder includes one or more of polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, acrylic acid-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-acrylate copolymer.

4. The current collector according to claim 1, wherein In the binder, the proportion of the number of the polar groups to the total number of functional groups is 40%-100%.

5. The current collector according to claim 1, characterized in that, The polyhydroxy compound includes polyhydric alcohol and polyphenol; The polyhydric alcohol includes water-soluble polyhydric alcohol; the water-soluble polyhydric alcohol includes one or more of xylitol, sorbitol, and polyvinyl alcohol; The polyphenol includes water-soluble polyphenol; the water-soluble polyphenol includes tannic acid.

6. The current collector according to claim 1, wherein, The metal ions include one or more of alkaline earth metal ions, group IIIA metal ions, and transition metal ions.

7. The current collector according to claim 1, wherein, The metal ions include Zn 2+ , Ca 2+ , Mg 2+ , Cu 2+ , Fe 3+ , Al 3+ or one or more of them.

8. The current collector according to claim 1, characterized in that, The metal ions are added to the conductive coating in the form of water-soluble metal salts, and the solid mass ratio of the conductive agent, binder, water-soluble metal salt, and polyhydroxy compound is 100: (15~120): (0~5): (0~10).

9. The current collector according to claim 8, wherein The solid mass ratio of the conductive agent, binder, water-soluble metal salt, and polyhydroxy compound is 100: (15~120): (0.2~5): (3~10).

10. The current collector according to claim 1, characterized in that, The conductive coating further includes a dispersant, and the dispersant includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, sodium carboxymethyl cellulose, polyacrylamide, and polyacrylic acid copolymers; The mass of the dispersant is 5%-30% of the mass of the conductive agent.

11. The current collector according to claim 1, wherein, The conductive agent includes one or more of acetylene black, carbon black, layered graphite, graphene, and carbon nanotubes; The thickness of the conductive coating is 0.5μm - 3μm.

12. A method for preparing a current collector according to any one of claims 1-11, characterized in that, It includes the following steps: Disperse at least one of a polyhydroxy compound and a water-soluble metal salt, as well as a binder and a conductive agent in an aqueous solvent to obtain a conductive paste; Coat the conductive paste on at least one side of the substrate, and after drying, obtain the current collector.

13. The method according to claim 12, characterized in that, The conductive paste further includes a dispersant, and the preparation of the conductive paste includes: dispersing at least one of a polyhydroxy compound and a water-soluble metal salt, as well as a binder, a conductive agent, and a dispersant in an aqueous solvent.

14. The method according to claim 12, wherein The water-soluble metal salts include one or more of nitrates, sulfates, and chlorides; the water-soluble metal salts include Zn 2+ , Ca 2+ , Mg 2+ , Cu 2+ , Fe 3+ , Al 3+ ; and one or more of the above The aqueous solvent includes water; The pH of the conductive paste is 4 - 9; The solid mass ratio of the conductive agent, binder, water-soluble metal salt, and polyhydroxy compound is 100 : (15~120): (0~5): (0~10); The solid content of the conductive paste is 2% - 20%.

15. A pole piece, characterized in that, It includes the current collector according to any one of claims 1 - 11.

16. A lithium-ion battery, characterized in that, It includes the electrode plate according to claim 15.

17. An electrical device, characterized in that, It includes the lithium-ion battery according to claim 16.

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